1. Field of the Invention
The present invention relates to damping structure for brake pad assemblies to inhibit brake squeal or noise, the invention having particular application to disk brakes.
2. Description of the Prior Art
In conventional brakes, particularly disk brakes, the frictional sliding between the brake shoe lining and the disk rotor may cause vibration of the brake shoe and of the other components coupled thereto, resulting in squealing or other noises. In order to suppress such noise, attempts have been made to fix a damping structure, including viscoelastic material, to the backing plate or shoe of the brake pad assembly to absorb or damp the noise-producing vibrations. Such damping structures have heretofore been provided on the outer or caliper side of the backing plate away from the friction lining.
The inventors of the present invention have determined that, for optimization of vibration damping performance, it is, in general, desirable for the damping structure to be disposed as closely as possible to the source of the vibrations, i.e., the interface between the rotor and the friction liner pad.
Applicants have further determined that the vibration or noise-damping performance of a damping structure, which is dependent on shearing of the viscoelastic material, is generally proportional to the surface area of the viscoelastic material. Heretofore, this surface area has been limited by the surface area of the backing plate to which the damping structure is attached.
Also, in prior damping arrangements which have been disposed on the outer surface of the backing plate, i.e., between the backing plate and the force-applying piston or caliper, the backing structure is subjected to torsional or rotational forces which can adversely affect performance. Furthermore, the area of contact with the piston is typically substantially less than the overall area of the damping structure. Thus, the damping structure has a tendency to become squeezed or compressed at the area of contact with the piston and has a tendency to lift or separate from the backing plate along the periphery thereof. Such prior damping arrangements have, in general, provided inadequate noise damping, particularly at lower frequencies.